1. Field of the Invention
The present invention relates to a linear movement table apparatus in which a table body assembled to a cylinder tube so as to be slidably moved in an axial direction is linearly driven through a feed screw mechanism and, in particular, to an improvement in the sliding function, the feed function, and the dust seal function of a linear movement table apparatus.
2. Description of the Prior Art
A prior art linear movement table apparatus of the present type is shown in Japanese Utility Model Laid-Open Publication No. 2-91251 filed by the Applicant's company. This apparatus is a rodless cylinder apparatus in which a piston located inside of the cylinder is linearly driven by a slide screw mechanism. As shown in FIG. 8, a cylinder tube 11 has a slit 12 formed by cutting open an upper side of the tube 11 in an axial direction. In the inside of the cylinder tube 11, a piston portion 23A made of a synthetic resin is assembled so as to be slidably movable in the axial direction. A part of the piston portion 23A protrudes to the outside of the cylinder tube 11 through the slit 12 to form a table portion 23B. Furthermore, the piston portion 23A has a pair of expanding guide portions which protrude respectively from both lateral sides of the piston portion 23A outwardly toward groove shaped guide surfaces 13a of the cylinder tube 11. Each of the expanding guide portions 1 has a split groove 2 so that the expanding guide portion 1 is elastically deformably fitted into the guide surface 13a. Furthermore, a screw shaft 21 is inserted in an axis portion of the cylinder tube 11, with opposite ends of the screw shaft 21 being rotatably supported by the cylinder tube 11. A feed nut 3 which is integrally formed with the piston portion 23A is threadedly engaged about the screw shaft 21 to constitute a slide screw mechanism.
When the screw shaft 21 is driven into rotation in a forward direction or in a reverse direction by a driving means, not shown, the table portion 23B is moved linearly back and forth through the feed nut 3 and, in turn, through the piston portion 23A, A seal band 35 closes the slit 12 to prevent dust from intruding into the inside of the cylinder tube 11. Since the seal band 35 extends through a band inserting bore 37 which is formed in the table portion 23B and curves upwardly in the axial direction, the table portion 23B can be moved while separating the seal band 35 from an upper surface of the cylinder tube 11.
In the prior art linear movement apparatus, the split groove 2 is formed in the expanding guide portion 1 of the piston portion 23A as a slide guide mechanism so that the expanding guide portion 1 is slidably and elastically deformably in contact with the guide surface of the cylinder tube 11. However, the length of the protrusion of the expanding guide portion 1 is restricted by the size of the inner width of the cylinder tube 11 such that the expanding guide portion 1 cannot protrude to a sufficient length. As a result, a problem is encountered in that the deflection limit of the expanding guide portion 1 is small and an adjustment for a dimensional error and wear of the cylinder tube 11 is not satisfactory such that the sliding movement function is insufficient.
Regarding the feed function, it is generally known that when the slide screw mechanism employed for feeding the piston portion 23A is imparted with a lateral force or a force moment, resistance is increased significantly resulting in an increase of driving torque. However, in the prior art apparatus, since the feed nut 3 of the slide screw mechanism and the piston portion 23A are integrally formed, there is a problem in that it is necessary to finish the screw shaft 21 with a very high accuracy and without bending or a lateral deviation of the shaft. Moreover, when there is a possibility that the piston portion 23A will be subjected to an excessively large lateral force, it is necessary to form the expanding guide portion 1 to provide high rigidity so as to prevent an external force from being applied to the screw mechanism. It is also necessary to form the cylinder tube 11 so as to have a very accurate inner width size. Accordingly, it is difficult to improve the productivity of the manufacture of the apparatus.
Furthermore, as to the dust sealing function, the intrusion of dust into the inside of the cylinder tube 11 is prevented by closing the slit 12 of the cylinder tube 11 by the seal band 35. However, since the table portion 23B must be moved while lifting the seal band 35 from the upper surface of the cylinder tube 11, the seal band 35 is separated from the cylinder surface at the position of the table portion 23B and the slit 12 is open. As a result, a problem is encountered in that the intrusion of dust into the inside of the cylinder tube 11 is permitted from the lateral sides of the table portion 23B.